Any discussion of background art, any reference to a document and any reference to information that is known, which is contained in this specification, is provided only for the purpose of facilitating an understanding of the background art to the present invention, and is not an acknowledgement or admission that any of that material forms part of the common general knowledge in Australia or any other country as at the priority date of the application in relation to which this specification has been filed.
Hot water storage units are used in domestic, commercial and other installations to store water that has been heated by a heater to produce heated water or hot water. The hot water is contained within a sealed vessel, or cylinder, of the hot water storage unit. The vessel is enclosed by an outer casing, which forms the exterior of the hot water storage unit. Various types and arrangements of heaters may be used for heating the water. In some systems, the heater may be provided inside the vessel, e.g. electrically powered heaters that employ heating elements inside the vessel to heat the water. In gas-powered systems, a gas burner is provided outside and beneath the vessel, inside the outer casing, to heat water in the vessel. In other systems, the heater may be provided outside the vessel and the outer casing, e.g. solar hot water systems and heat pump systems may employ such an arrangement.
Such hot water storage units are provided with a valve to relieve excess pressure and/or temperature from inside the vessel by allowing water to escape from inside the vessel. They are often referred to as PTR valves, i.e. pressure-temperature relief valves. If the pressure and/or temperature inside the vessel reaches, or exceeds, the (set) pressure and/or temperature to which the PTR valve has been set, the PTR valve will open and water will be able to escape from the vessel via the (open) PTR valve. The PTR valve is provided as a safety mechanism to ensure that potentially hazardous excess temperatures and/or pressures do not build up inside the vessel.
A conventional hot water storage unit 10 is shown in FIGS. 1A to 1C. The conventional hot water storage unit 10 comprises a vessel 12, an outer casing 14 that encloses the vessel 12, insulation material 16 that is provided between the vessel 12 and the outer casing 14, and a conventional PTR valve 18. The PTR valve 18 has a body 20 that contains the operational components of the PTR valve 18. The body 20 also incorporates a drain 22. If the temperature and/or pressure of the water inside the vessel 12 reaches or exceeds the set pressure and/or temperature of the PTR valve, the PTR valve opens and water can exit from the PTR valve 18, via the drain outlet 24, to reduce the temperature and/or pressure of the water inside the vessel. For example, the temperature of the water in the vessel may be sensed by a probe 28. When the pressure and/or temperature falls below the set pressure and/or temperature of the PTR valve, the PTR valve closes. The body 20 may also incorporate an auxiliary relief device 26. When the PTR valve 18 is connected with the hot water storage unit 10, usually by a screw thread arrangement (as is shown in FIGS. 1A to 1C), the part of the body 20, that contains the operational components of the PTR valve 18, is located outside the outer casing 14. As can be seen from FIGS. 1A to 1C, this results in a substantial portion of the body 20 of the PTR valve 18 being located outside the outer casing 14. This gives rise to a number of problems and disadvantages.
Firstly, having the PTR valve located outside the outer casing of conventional hot water storage units means that PTR valve projects out from the side of the otherwise even outer casing and is susceptible to damage when the hot water storage unit is in transit, i.e. from the time of manufacture of the hot water storage unit until the time of installation at the required site. For this reason, manufacturers do not usually factory-fit the PTR valve. Instead, the hot water storage unit leaves the factory without the PTR valve fitted. Manufacturers provide the PTR valve separately for later installation by the installer, e.g. a plumber, at the time of installation of the hot water storage unit at the required site, e.g. a domestic, commercial or other installation site.
In addition, because the hot water storage unit leaves the factory without the PTR valve fitted, the manufacturer cannot perform a pressure test of the vessel to provide quality assurance that the vessel meets the required operating standards since the water storage unit would have to leave the factory with the PTR valve fitted for such quality assurance to be validly given by the manufacturer.
Furthermore, problems can arise when the PTR valve is provided separately and is installed by the installer, e.g. a plumber, at the time of installation of the hot water storage unit at the required site. This is because the PTR valve must be connected with the hot water storage unit such that the outlet of the drain is orientated downwardly, at a suitable angle, so that water exiting the PTR valve falls away from the drain and does not pool in the drain. This requires one or more attempts by the installer to connect the PTR valve, using different amounts of thread tape on the screw thread of the PTR valve, until the outlet of the drain is orientated downwardly, at a suitable angle, and the PTR valve is securely attached (i.e. that the connection between the PTR valve and the hot water storage unit does not leak, which itself cannot be assured until the hot water storage unit is actually operating, which is itself disadvantageous). However, this process can be a time-consuming for the installer, requiring several attempts merely to properly connect the PTR valve with the hot water storage unit.
In addition to the time consumed, problems may also arise if the connection of the PTR valve with the hot water storage unit is over or under tightened. Over-tightening may result in damage to components, such as the screw threads on the PTR valve or the hot water storage unit. Under-tightening may result in improper sealing at the connection, with consequential leakage of water from the vessel. Each of these may be perceived as a fault by the consumer, necessitating a service call from the consumer to the manufacturer or a service agent to properly connect or to replace the PTR valve. This is inconvenient and an annoyance for the consumer and is time-consuming and costly for the manufacturer or service agent having to attend the service call.
A further disadvantage of having a substantial portion of the body of the PTR valve located outside the outer casing is that heat loss occurs from the heated water inside the vessel, through the body of PTR valve, and to the ambient air outside the outer casing. Indeed, this has resulted in manufacturers of PTR valves using separate insulation casings to enclose the portion of the body of the PTR valve located outside the outer casing to thereby reduce heat losses.
Conventional hot water storage units suffer from another disadvantage in that, to accommodate the different thicknesses of insulation that may be used in different units, the probes (28) must be made in a range of lengths so that they are of sufficient length to extend into the water in the vessel (12).